The present invention is directed to inks and to methods for the use thereof. More specifically, the present invention is directed to inks and ink sets for use in ink jet printing processes, wherein intercolor bleed between the inks is reduced. One embodiment of the present invention is directed to an ink composition which comprises water, an anionic dye, and a monoquaternary cationic penetrant of the formula ##STR2## wherein R.sub.1 is either a benzyl group or an alkyl group having at least about 3 carbon atoms, R.sub.2, R.sub.3, and R.sub.4 each, independently of the others, are hydrogen atoms, methyl groups, or ethyl groups, wherein two or more R groups can be joined together to form a ring, X is an anion, and n is an integer representing the charge on the anion, wherein the ink exhibits rapid penetration when applied to plain paper. Another embodiment of the present invention is directed to a process which comprises applying an ink composition which comprises water, an anionic dye, and a monoquaternary cationic penetrant of the formula ##STR3## wherein R.sub.1 is either a benzyl group or an alkyl group having at least about 3 carbon atoms, R.sub.2, R.sub.3, and R.sub.4 each, independently of the others, are hydrogen atoms, methyl groups, or ethyl groups, wherein two or more R groups can be joined together to form a ring, X is an anion, and n is an integer representing the charge on the anion, to a plain paper substrate, wherein the ink exhibits rapid penetration of the substrate. Yet another embodiment of the present invention is directed to a set of inks for generating multicolored images which comprises (a) a first ink comprising water, an anionic dye, and a monoquaternary cationic penetrant of the formula ##STR4## wherein R.sub.1 is either a benzyl group or an alkyl group having at least about 3 carbon atoms, R.sub.2, R.sub.3, and R.sub.4 each, independently of the others, are hydrogen atoms, methyl groups, or ethyl groups, wherein two or more R groups can be joined together to form a ring, X is an anion, and n is an integer representing the charge on the anion; and (b) a second ink comprising water and a pigment; wherein intercolor bleed between the first ink and the second ink is reduced. Still another embodiment of the present invention is directed to a process for generating multicolored images on a recording sheet which comprises (a) providing a first ink comprising water, an anionic dye, and a monoquaternary cationic penetrant of the formula ##STR5## wherein R.sub.1 is either a benzyl group or an alkyl group having at least about 3 carbon atoms, R.sub.2, R.sub.3, and R.sub.4 each, independently of the others, are hydrogen atoms, methyl groups, or ethyl groups, wherein two or more R groups can be joined together to form a ring, X is an anion, and n is an integer representing the charge on the anion; (b) providing a second ink comprising water and a pigment; (c) applying the first ink to the recording sheet; and (d) applying the second ink to the recording sheet; wherein the first ink is in contact with the second ink on the recording sheet, and wherein intercolor bleed between the first ink and the second ink is reduced.
Ink jet printing systems generally are of two types: continuous stream and drop-on-demand. In continuous stream ink jet systems, ink is emitted in a continuous stream under pressure through at least one orifice or nozzle. The stream is perturbed, causing it to break up into droplets at a fixed distance from the orifice. At the break-up point, the droplets are charged in accordance with digital data signals and passed through an electrostatic field which adjusts the trajectory of each droplet in order to direct it to a gutter for recirculation or a specific location on a recording medium. In drop-on-demand systems, a droplet is expelled from an orifice directly to a position on a recording medium in accordance with digital data signals. A droplet is not formed or expelled unless it is to be placed on the recording medium.
Since drop-on-demand systems require no ink recovery, charging, or deflection, the system is much simpler than the continuous stream type. There are two types of drop-on-demand ink jet systems. One type of drop-on-demand system has as its major components an ink filled channel or passageway having a nozzle on one end and a piezoelectric transducer near the other end to produce pressure pulses. The relatively large size of the transducer prevents close spacing of the nozzles, and physical limitations of the transducer result in low ink drop velocity. Low drop velocity seriously diminishes tolerances for drop velocity variation and directionality, thus impacting the system's ability to produce high quality copies. Drop-on-demand systems which use piezoelectric devices to expel the droplets also suffer the disadvantage of a slow printing speed.
Another type of drop-on-demand system is known as thermal ink jet, or bubble jet, and produces high velocity droplets and allows very close spacing of nozzles. The major components of this type of drop-on-demand system are an ink filled channel having a nozzle on one end and a heat generating resistor near the nozzle. Printing signals representing digital information originate an electric current pulse in a resistive layer within each ink passageway near the orifice or nozzle, causing the ink in the immediate vicinity to evaporate almost instantaneously and create a bubble. The ink at the orifice is forced out as a propelled droplet as the bubble expands. When the hydrodynamic motion of the ink stops, the process is ready to start all over again. With the introduction of a droplet ejection system based upon thermally generated bubbles, commonly referred to as the "bubble jet" system, the drop-on-demand ink jet printers provide simpler, lower cost devices than their continuous stream counterparts, and yet have substantially the same high speed printing capability.
The operating sequence of the bubble jet system begins with a current pulse through the resistive layer in the ink filled channel, the resistive layer being in close proximity to the orifice or nozzle for that channel. Heat is transferred from the resistor to the ink. The ink becomes superheated far above its normal boiling point, and for water based ink, finally reaches the critical temperature for bubble formation or nucleation of around 280.degree. C. Once nucleated, the bubble or water vapor thermally isolates the ink from the heater and no further heat can be applied to the ink. This bubble expands until all the heat stored in the ink in excess of the normal boiling point diffuses away or is used to convert liquid to vapor, which removes heat due to heat of vaporization. The expansion of the bubble forces a droplet of ink out of the nozzle, and once the excess heat is removed, the bubble collapses on the resistor. At this point, the resistor is no longer being heated because the current pulse has passed and, concurrently with the bubble collapse, the droplet is propelled at a high rate of speed in a direction towards a recording medium. The resistive layer encounters a severe cavitational force by the collapse of the bubble, which tends to erode it. Subsequently, the ink channel refills by capillary action. This entire bubble formation and collapse sequence occurs in about 10 microseconds. The channel can be refired after 100 to 500 microseconds minimum dwell time to enable the channel to be refilled and to enable the dynamic refilling factors to become somewhat dampened. Thermal ink jet processes are well known and are described in, for example, U.S. Pat. No. 4,601,777, U.S. Pat. No. 4,251,824, U.S. Pat. No. 4,410,899, U.S. Pat. No. 4,412,224, and U.S. Pat. No. 4,532,530, the disclosures of each of which are totally incorporated herein by reference.
Acoustic ink jet printing processes are also known. As is known, an acoustic beam exerts a radiation pressure against objects upon which it impinges. Thus, when an acoustic beam impinges on a free surface (i.e., liquid/air interface) of a pool of liquid from beneath, the radiation pressure which it exerts against the surface of the pool may reach a sufficiently high level to release individual droplets of liquid from the pool, despite the restraining force of surface tension. Focusing the beam on or near the surface of the pool intensifies the radiation pressure it exerts for a given amount of input power. These principles have been applied to prior ink jet and acoustic printing proposals. For example, K. A. Krause, "Focusing Ink Jet Head," IBM Technical Disclosure Bulletin, Vol. 16, No. 4, September 1973, pp. 1168-1170, the disclosure of which is totally incorporated herein by reference, describes an ink jet in which an acoustic beam emanating from a concave surface and confined by a conical aperture was used to propel ink droplets out through a small ejection orifice. Acoustic ink printers typically comprise one or more acoustic radiators for illuminating the free surface of a pool of liquid ink with respective acoustic beams. Each of these beams usually is brought to focus at or near the surface of the reservoir (i.e., the liquid/air interface). Furthermore, printing conventionally is performed by independently modulating the excitation of the acoustic radiators in accordance with the input data samples for the image that is to be printed. This modulation enables the radiation pressure which each of the beams exerts against the free ink surface to make brief, controlled excursions to a sufficiently high pressure level for overcoming the restraining force of surface tension. That, in turn, causes individual droplets of ink to be ejected from the free ink surface on demand at an adequate velocity to cause them to deposit in an image configuration on a nearby recording medium. The acoustic beam may be intensity modulated or focused/defocused to control the ejection timing, or an external source may be used to extract droplets from the acoustically excited liquid on the surface of the pool on demand. Regardless of the timing mechanism employed, the size of the ejected droplets is determined by the waist diameter of the focused acoustic beam. Acoustic ink printing is attractive because it does not require the nozzles or the small ejection orifices which have caused many of the reliability and pixel placement accuracy problems that conventional drop on demand and continuous stream ink jet printers have suffered. The size of the ejection orifice is a critical design parameter of an ink jet because it determines the size of the droplets of ink that the jet ejects. As a result, the size of the ejection orifice cannot be increased, without sacrificing resolution. Acoustic printing has increased intrinsic reliability because there are no nozzles to clog. As will be appreciated, the elimination of the clogged nozzle failure mode is especially relevant to the reliability of large arrays of ink ejectors, such as page width arrays comprising several thousand separate ejectors. Furthermore, small ejection orifices are avoided, so acoustic printing can be performed with a greater variety of inks than conventional ink jet printing, including inks having higher viscosities and inks containing pigments and other particulate components. It has been found that acoustic ink printers embodying printheads comprising acoustically illuminated spherical focusing lenses can print precisely positioned pixels (i.e., picture elements) at resolutions which are sufficient for high quality printing of relatively complex images. It has also has been discovered that the size of the individual pixels printed by such a printer can be varied over a significant range during operation, thereby accommodating, for example, the printing of variably shaded images. Furthermore, the known droplet ejector technology can be adapted to a variety of printhead configurations, including (1) single ejector embodiments for raster scan printing, (2) matrix configured ejector arrays for matrix printing, and (3) several different types of pagewidth ejector arrays, ranging from single row, sparse arrays for hybrid forms of parallel/serial printing to multiple row staggered arrays with individual ejectors for each of the pixel positions or addresses within a pagewidth image field (i.e., single ejector/pixel/line) for ordinary line printing. Inks suitable for acoustic ink jet printing typically are liquid at ambient temperatures (i.e., about 25.degree. C.), but in other embodiments the ink is in a solid state at ambient temperatures and provision is made for liquefying the ink by heating or any other suitable method prior to introduction of the ink into the printhead. Images of two or more colors can be generated by several methods, including by processes wherein a single printhead launches acoustic waves into pools of different colored inks. Further information regarding acoustic ink jet printing apparatus and processes is disclosed in, for example, U.S. Pat. No. 4,308,547, U.S. Pat. No. 4,697,195, U.S. Pat. No. 5,028,937, U.S. Pat. No. 5,041,849, U.S. Pat. No. 4,751,529, U.S. Pat. No. 4,751,530, U.S. Pat. No. 4,751,534, U.S. Pat. No. 4,801,953, and U.S. Pat. No. 4,797,693, the disclosures of each of which are totally incorporated herein by reference. The use of focused acoustic beams to eject droplets of controlled diameter and velocity from a free-liquid surface is also described in J. Appl. Phys., vol. 65, no. 9 (1 May 1989) and references therein, the disclosure of which is totally incorporated herein by reference.
U.S. Pat. No. 5,019,166 (Schwarz), the disclosure of which is totally incorporated herein by reference, discloses a thermal ink jet printing composition comprising a dye, a liquid medium, and a surfactant selected from the group consisting of polyoxyalkylated ethers, anionic bitail fluorothio alkyls, alkyl aryl sulfonates, alkyl amine quaternary salts, and mixtures thereof. Also disclosed is a process for generating images which comprises causing the ink compositions disclosed herein to be ejected from a thermal ink jet printer in imagewise fashion onto a substrate.
Copending application U.S. Ser. No. 09/046,895, filed Mar. 24, 1998, entitled "Ink Compositions and Multicolor Thermal Ink Jet Printing Process for the Production of High Quality Images," with the named inventor John Wei-Ping Lin, the disclosure of which is totally incorporated herein by reference, discloses a set of inks for printing multicolor images in an ink jet printer, said ink set comprising (A) a first ink having a first color and comprising water and a colorant selected from the group consisting of (1) anionic dyes, (2) dyes having physical or chemically associated therewith a stabilizing agent having anionic groups thereon, (3) pigment particles having anionic groups chemically attached thereto, (4) pigment particles having physically or chemically associated therewith a stabilizing agent having anionic groups thereon, and (5) mixtures thereof; and (B) a second ink comprising water, an optional colorant having a color other than the first color, and an ammonium salt having at least two cationic ammonium functional groups, wherein the colorant in the first ink is capable of being immobilized on a printing substrate by interaction with the ammonium salt having at least two cationic ammonium functional groups in the second ink.
Copending application U.S. Ser. No. 09/047,097, filed Mar. 24, 1998, entitled "Ink Compositions With Improved Waterfastness and Smear Resistance," with the named inventors Kurt B. Gundlach, Richard L. Colt, Luis A. Sanchez, Maura A. Sweeney, and Edward J. Radigan, Jr., the disclosure of which is totally incorporated herein by reference, discloses an ink composition which comprises water, an anionic dye, and a polyquaternary amine compound selected from the group consisting of polydiallyl dimethyl ammonium compounds, polyquaternized polyvinylamines, polyquaternized polyallylamines, and mixtures thereof. Also disclosed are methods for using the aforementioned ink composition in ink jet printing processes.
Copending application U.S. Ser. No. 09/046,852, filed Mar. 24, 1998, entitled "Ink Compositions With Improved Shelf Stability", with the named inventors Kurt B. Gundlach, Luis A. Sanchez, Richard L. Colt, Maura A. Sweeney, and William M. Schwarz, the disclosure of which is totally incorporated herein by reference, discloses an ink composition which comprises (1) water; (2) a nonpolymeric salt comprising at least one cation and at least one anion; and (3) a colorant comprising an anionic dye complexed with a polyquaternary amine compound. Also disclosed is an ink composition which comprises (1) water; (2) a nonpolymeric salt comprising at least one cation and at least one anion; (3) an anionic dye; and (4) a polyquaternary amine compound. In one embodiment, the polyquaternary amine compound is selected from the group consisting of polydiallyl dimethyl ammonium compounds, polyquaternized polyvinylamines, polyquaternized polyallylamines, epichlorohydrin/amine copolymers, cationic amido amine copolymers, copolymers of vinyl pyrrolidinone and a vinyl imidazolium salt, and mixtures thereof.
Copending application U.S. Ser. No. 09/046,849, filed Mar. 24, 1998, entitled "Ink Compositions Containing Cationic Amido Amine Polymers", with the named inventor William M. Schwarz, the disclosure of which is totally incorporated herein by reference, discloses an ink composition which comprises (1) water; (2) a dye; and (3) a cationic amido amine copolymer. Also disclosed are methods for using the aforementioned ink composition in ink jet printing processes.
Copending application U.S. Ser. No. 09/047,278, filed Mar. 24, 1998, entitled "Ink Compositions Containing Vinyl Pyrrolidinone/Vinyl Imidazolium Copolymers", with the named inventor William M. Schwarz, the disclosure of which is totally incorporated herein by reference, discloses an ink composition which comprises (1) water; (2) an anionic dye; and (3) a copolymer of vinyl pyrrolidinone and a vinyl imidazolium salt. Also disclosed are methods for using the aforementioned ink compositions in ink jet printing processes.
Copending application U.S. Ser. No. 09/106,391; entitled "Ink Compositions Containing Oxy Acids or Oxy Acid Salts," with the named inventor William M. Schwarz, filed concurrently herewith, the disclosure of which is totally incorporated herein by reference, discloses an ink composition which comprises (1) water; (2) a colorant; and (3) an additive selected from the group consisting of oxy acids, oxy acid salts, and mixtures thereof. Also disclosed is a thermal ink jet printing process employing the ink.
Copending application U.S. Ser. No. 09/106,396; entitled "Ink Compositions Containing Ionic Liquid Solvents," with the named inventor William M. Schwarz, filed concurrently herewith, the disclosure of which is totally incorporated herein by reference, discloses an ink composition which comprises water, a colorant, and an ionic liquid material. In a preferred embodiment, the ink is substantially free of organic solvents. Also disclosed is a process which comprises incorporating the ink composition into an ink jet printing apparatus and causing droplets of the ink composition to be ejected in an imagewise pattern onto a substrate.
Copending application U.S. Ser. No. 09/106,621; entitled "Ink Compositions Substantially Free of Organic Liquids," with the named inventors Kurt B. Gundlach, Maura A. Sweeney, Luis A. Sanchez, Richard L. Colt, and Melvin D. Croucher, filed concurrently herewith, the disclosure of which is totally incorporated herein by reference, discloses an ink composition which comprises water, an acid dye, a monovalent salt, a polyquaternary amine compound, and an optional surfactant, said ink being substantially free of organic solvents. The ink is particularly suitable for applications such as ink jet printing and marking pens. The disclosed inks in some embodiments are substantially indelible. Also disclosed is a composition for removing the ink compositions from substrates to which they have been applied which comprises water and a dianionic surfactant, optionally further containing a salt, urea, and/or a viscosity building agent such as a gum.
While known compositions and processes are suitable for their intended purposes, a need remains for improved ink compositions for ink jet printing. In addition, a need remains for ink compositions which exhibit reduced intercolor bleed when printed adjacent to each other or on top of each other. Further, a need remains for ink compositions which exhibit reduced edge raggedness, feathering, and MFLEN, particularly when printed on plain paper. Additionally, a need remains for inks with desirable substrate penetrating characteristics. There is also a need for inks which exhibit reduced wet and dry smear characteristics. In addition, there is a need for ink compositions with good waterfastness characteristics. Further, there is a need for ink compositions with desirable substrate wetting characteristics.